1. Field of the Invention
The present invention relates to a method of a surface treatment in improving adhesion of an organic polymeric low-k dielectric layer, and more particularly, to a method of enhancing a protective layer/adhesion promoter coating (APC) interface and an adhesion promoter coating/organic polymeric low-k dielectric layer interface.
2. Background of the Invention
With a decreasing size of semiconductor devices and an increase in integrated circuit (IC) density, RC time delay, produced between metal wires, seriously affects IC performance and reduces IC working speed. RC time delay effects are more obvious especially when the line width is reduced to 0.25 xcexcm, or even 0.15 xcexcm, in a semiconductor process. Because, RC time delay produced between metal wires is a product of electrical resistance (R) of the metal wires and parasitic capacitance (C) of the dielectric layer between the metal wires. However, there are two approaches to reduce RC time delay: a) using conductive materials with a lower resistance as a metal wire or, b) reducing the parasitic capacitance of the dielectric layer between metal wires.
In the approach of using a metal wire with a lower resistance, copper interconnection technology replaces the traditional Al:Cu(0.5%) alloy fabrication process and is a necessary tendency in multilevel metallization processes. Due to copper having a low resistance (1.67 xcexcxcexa9-cm) and higher current density load without electro-migration in the Al/Cu alloy, the parasitic capacitance between metal wires and connection levels of metal wires is reduced.
Additionally, in order to reduce the parasitic capacitance of a dielectric layer between metal wires, it is a trend to adopt low-k dielectric materials. SiLK(trademark) resin, specifically developed by Dow Chemical Company, features a low isotropic dielectric constant of 2.65, 40 percent lower than that of silicon dioxide, the traditional interlayer dielectric material. SiLK(trademark) resin has no fluorine in its composition, which prevents contamination of metal barrier levels. Moreover, SiLK(trademark) resin is stable at temperatures up to 450xc2x0 C., which provides a wide processing window. As a result, SiLK(trademark) resin is a promising low-k dielectric material in the present day and the integration between SiLK(trademark) resins and copper metal wires is very important. Adhesion between SiLK(trademark) resins and other films, such as cap layers, will particularly influence electrical performance or reliability of metal interconnection technology.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of coating an organic polymeric low-k dielectric layer according to the prior art. As shown in FIG. 1, a semiconductor wafer 10 comprises an underlying conductive region 11, encased in an insulator layer 12. A protective layer 13 is deposited on the underlying conductive region 11 and the insulator layer 12. The protective layer 13, composed of silicon nitride (SiN) or silicon carbide (SiC), is used to prevent conductor atoms in the underlying conducting region 11, such as copper atoms, from migrating into dielectric layers. Additionally, the protective layer 13 also serves as an etch stop layer. An adhesion promoter coating layer 14 is deposited on the surface of the protective layer 13 and a SiLK(trademark) layer 15 is formed on the adhesion promoter coating layer 14. The adhesion promoter coating layer 14 will enhance adhesion between the SiLK(trademark) layer 15 and the underlying layer, formed of a material such as silicon, silicon dioxide, silicon nitride, aluminum, tantalum, tantalum nitride and titanium nitride.
The adhesion promoter coating layer 14 is made of an AP4000 adhesion promoter, produced by Dow Chemical Company. The AP4000 adhesion promoter is a kind of solution, which dissolves adhesion promoter molecules into an organic solvent, 1-methoxy-propanol acetate, to form an adhesion promoter solution with a concentration lower than 3%. In general, a way to form the adhesion promoter coating layer 14 is to flood the wafer surface with the adhesion promoter solution before depositing the SiLK(trademark) layer and then spin it dry. After coating, the adhesion promoter coating layer 14 should be baked and then, the formation of the adhesion promoter coating layer 14 is completed.
SiLK(trademark) resin basically is an aromatic hydrocarbon polymer, which is a hydrophobic material, and an adhesion promoter molecule is composed of at least one hydrophilic group and one hydrophobic group. Ideally, when coating the adhesion promoter coating layer 14 on the protective layer 13, the hydrophilic groups of adhesion promoter molecules will combine with the protective layer 13 while the hydrophobic groups of adhesion promoter (AP) molecules will turn upward. FIG. 2 is the enlarged structural schematic diagram of the adhesion promoter coating layer, the protective layer and the SiLK(trademark) layer. Therein, A represents a hydrophilic group in an AP molecule, B represents a hydrophobic group in an AP molecule, and C represents other elements in an AP molecule. However, the surface of the protective layer 13 is not perfectly hydrophilic, so that orientation of the hydrophilic groups and the hydrophobic groups in the adhesion promoter molecules is irregular, which reduces the effectiveness of the adhesion between the adhesion promoter coating layer 14 and the SiLK(trademark) layer 15. Further, electrical performance or reliability of metal interconnection technology is reduced.
It is therefore a primary objective of the present invention to provide a method of a surface treatment that enhances a protective layer/adhesion promoter coating interface and an adhesion promoter coating/organic polymeric low-k dielectric layer interface.
According to the preferred embodiment of the present invention, a protective layer composed of silicon nitride (SiN) or silicon carbide (SiC) is deposited on a substrate. Then, a hydrophilic surface is produced across the top surface by performing a fast surface treatment that subjects a top surface of the protective layer to an oxygen-containing plasma at a pre-selected low radio frequency (RF) power. An adhesion promoter coating is formed over the plasma-treated top surface of the protective layer, and the adhesion promoter coating is comprised of adhesion promoter molecules, each adhesion promoter molecule having at least one hydrophobic group and one hydrophilic group. An organic polymeric low-k dielectric layer is spin-on coated onto the adhesion promoter coating. Wherein, the formation of the hydrophilic surface alters an orientation of the promoter molecules to facilitate the hydrophilic group of each of the promoter molecules in facing the hydrophilic surface while the hydrophobic group of each of the promoter molecules faces the organic polymeric low-k dielectric layer, thereby simultaneously enhancing the protective layer/adhesion promoter coating interface and the adhesion promoter coating/organic polymeric low-k dielectric layer interface.
It is an advantage of the present invention that it provides a method of a surface treatment that enhances the protective layer/adhesion promoter coating interface and the adhesion promoter coating/organic polymeric low-k dielectric layer interface.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.